1. Field of the Invention
The invention relates to the field of automated conveyance. More particularly the invention relates to a positioning method and apparatus. In still greater particularity, the invention relates to a track and car system utilizing a combination of apertures and spaces on a rail to accurately position a plurality of automated cars.
2. Description of the Related Art
Many measuring and testing instruments, as for example, immunonephelometric instruments, such as that described in U.S. Pat. No. 4,157,871 issued on June 12, 1979, and incorporated herein by reference, require successive manipulations of a sample substance to be tested. In addition, pending application U.S. S.N. 141,455 discloses other details of this system and is incorporated by reference. That application is assigned to the same assignee as this application and the above U.S. Patent. These manipulations consume a great deal of operator time when a number of assays on many samples are performed. To obtain good results, an operator must repeat a number of steps in the proper sequence for each sample. Manual pipetting steps include the identification of a number of samples as well as numerous sample dilutions. Because the sample manipulations are usually done manually, operator fatigue and boredom often result in erroneous results. Additionally, reduced operator morale due to fatigue and boredom generally contributes to a decrease in job performance resulting in increased operating costs for the laboratory. Also, manual manipulations consume a great deal of time often resulting in long delays to obtain results.
Automated sample handling systems have been used to replace the manual sample manipulations previously relied on. In such systems, one or more automated cars or robots are employed. One problem with these systems is the positioning of the robots to perform the operations. That is, exact positioning of the robots to allow access of a pipette to a sample cup or other container is difficult to achieve. The precision required results in the use of expensive sensors and costly systems. In addition, the systems have been subject to errors should the robots get lost on the track. Thus continual monitoring and repositioning of a car has been required with prior systems. Errors may also be introduced into the system by interference such as dirt or scratches on the track. That is, where apertures are used on the track as position determinations, dirt or other foreign material may interfere with the apertures. These problems are especially acute where narrow apertures are used in precise positioning apparatus. When, as with most systems, counting is used, the nondetection of an aperture will result in the robot stopping at the wrong aperture. This error will carry through and will result in continually incorrect results. In addition, should a robot in one of the systems be bumped or otherwise interfered with, the system would have to be shut down and the cars manually repositioned to ensure accuracy. It would be desirable to have a robot positioning system which would be "smart" enough to know its position and which could verify its position continuously to ensure that each car remains accurately positioned.
The above problems are especially acute in an automated sample handling system utilized by an automated clinical diagnostic instrument. In such a system the cars move back and forth along the track and the cars must cover relatively large distances accurately. Because incorrect positioning could yield an incorrect result, possibly resulting in a wrong diagnosis for a patient, these cars must recognize their relative position on the guide track at all times.